Grid glow tube



P D. D. KNOWLES ,4

GRID GLOW TUBE Filed Sept. 23, 1953 WITNESSES: INV ENTOR ATTORNEY inted Penn lva ia Application September23, 19313.saalmfi oim Claims. (c .;1*:s' s54 Myinvention relates'to, ayapor-lelectric con verter and particularly toanexcitation system for such a converter. I

In the operation of vapor electric converters, considerable trouble has beenexperienced because of inverse current carrying arcsor sofcalled back-fires in the converters. Ihave found that one of the principal causes of back.-'firing is the presence in the converter during the inverse-or inactive half cycle of large quantities of; ionized vapor. u

It has heretofore been-proposed to eliminate the creation of ionization during the inverse half cycle by providing a make-alive electrode operative at the beginning of each active half cycle to create a cathode spot in the converter. This make-alive system, however, has the disadvantage that at the crest of the forward current a relatively high current is present in make-alive electrode. This trouble is particularly prevalent in grid control devices such as grid-glow tubes, in which the main current carrying arc may be established late in the active half cycle.

it is object of 'my invention to provide an excitation system requiring a relative low excitation current during that portion of the positive half cycle in which the main electrodes are substantially inactive and which are inoperative on the inverse half cycle.

it is a further object of my invention to provide an excitation system having a make-alive electrode for initiating the cathode spot and a keep alive electrode for maintaining said spot until it is required to establish the arc between the main electrodes.

the construction according to my invention, a vapor electric device is provided with a plurality of auxiliary or excitation anodes connected in parallel and preferably fed from the anode supply circuit through a suitable current limiting device.

Gther objects and advantages of my invention will be apparent from the. accompanying drawing in which the single figure is a schematic illustration of a grid-glow tube embodying my invention.

The apparatus according to my invention comprises a suitable evacuated chamber 6 having a cathode of vaporizable material cooperating with a suitable anode El. Suitable control grids i and 55 are interposed between the anode 3 and the cathode 2 to control the formation of the rectifying arc in the converter.

The grid t is a'deionizing grid while grid 5 is provided with an outside terminal for connection to any suitable control system (not shown).

X Alternating current is suppliedfronr a suitable 1 source such as a transformer 6,.the direct-current consuming device T beinglocated between the transformer 6 and one of themainelectrodes. A suitable make-aliveelectrode [Dis inserted in the rectifying chamber in contact with the ,vaporizing. cathode. The make-alive electrode I0 is supplemented bya suitablev keepealive electrode l l spaced from the cathode. Each of these auxiliary electrodes is connected to the alternating-current source 6 through a suitable current limiting device, such as a resistor l2. A suitable uni-directional conductor 83 such as a copper oxide rectiher or an arc-discharge tube is placed between the excitation source it and the make-alive electrode it.

In the operation of my device alternating cur= rent is applied to the main electrodes 2-3 of the converter and when the potential applied to the anode 3 is positive, the positive potential will flow through the uni-directional conductor l3 to the make-alive electrode ill which initiates a cathode spot on the vaporizable material 2. As soon as this spot has been initiated current will start to iiow from the keep-alive electrode i l. 1 Since this keep-alive electrode is connected in parallel with. the make-alive electrode ill the low arc drop be tween the keep-alive electrode and the cathode will reduce the potential applied to the maize alive so that substantially no current will be carried thereby. In order to prevent an excessive flow of current through the auxiliary electrode, a suitable current limiting resistor i2 is placed be tween the auxiliary electrodes and the anode circult. After the cathode spot has been initiated it will be maintained by the keep-alive electrode it until the control grid 55 is released, allowing current to flow between the main electrodes 2 and oi the device.

At the termination of the positive halt cycle the current between the main electrodes and also the auxiliary electrodes will pass through zero and both the excitation and main arc will be extinguished. The uni-directional current carrying device it in series with the make-alive electrode it prevents inverse current how throughout the negative half cycle, and con sequently, no arc or cathode spot will be present during this inverse half cycle. As a consequence, there is little, if any, ionization present to produce the undesirable back current to the anode during the inactive period.

For purposes of illustration, I have shown. a specific embodiment of my invention. However,

till

it will 'be apparent to those skilled in the art 55 that changes and modifications can be made therein without departing from the true spirit of my invention or the scope of the appended claims.

I claim as my invention:

1. An arc discharge device comprising, a plurality of main electrodes, a control electrode for controlling the discharge between the main electrodes, a plurality of auxiliary electrodes for producing a cathode spot on one of said main electrodes, one of said auxiliary electrodes being operative to initiate a cathode spot and another to maintain said cathode spot until the control electrode operates to start the main arc, and means for inhibiting operation of the auxiliary electrodes when inverse potential is applied between said main electrodes.

2. An electrical conversion system comprising a source of alternating current, a direct current load fed thereby, a grid-controlled converter,a plurality of main electrodes in said converter at least one of said electrodes being of vaporizable material, a grid for controlling the discharge between said main electrodes, a make-alive electrode for initiating a cathode spot on one of said main electrodes, a keep-alive electrode connected in parallel with said make-alive and a source of potential connected to said makealive and keep-alive electrodes.

3. An electric valve comprising an anode, a cathode cooperating with said anode, a. starting electrode in contact with said cathode, a keepalive electrode spaced from said cathode, means ,for applying positive potential to said starting electrode and said keep-alive electrode simultaneously with application of positive potential to said anode, said starting electrode acting to initiate a cathode spot on said cathode upon the application of positive potential to said electrodes, said keep-alive electrode being operative to maintain said cathode spot during the application of positive potential thereto, means con nected in series with said starting electrode for rendering said starting electrode inactive during operation of said keep-alive electrode, said means preventing operation of said starting electrode during application of negative potential to said electrodes.

4. An electric valve comprising an anode, a cathode cooperating with said anode, a starting electrode in contact with said cathode, a keepalive electrode spaced from said cathode, means for applying positive potential to said starting electrode and said keep-alive electrode simultaneously with application of positive potential to said anode, said starting electrode acting to initiate a cathode spot on said cathode upon the application of positive potential to said electrodes, said keep-alive electrode being operative to maintain said cathode spot during the application of positive potential thereto, means connected in series with said starting electrode for rendering said starting electrode inactive during operation of said keep-alive electrode, said means preventing operation of said starting electrode during application of negative potential to said electrodes, and a control electrode associated with said anode for controlling the formation of a current-carrying arc to said anode.

DEWEY D. KNOWLES. 

